1. Field of the Invention
The present invention relates to an endless track of the type having a ground opposing surface made from urethane rubber and a manufacturing method thereof.
2. Description of Related Art
Various types of endless tracks used for construction vehicles are known, some of which include a ground opposing surface made from rubber for protecting road surfaces.
Such conventional endless tracks of the type having a ground opposing surface made from rubber are grouped into the following three categories:
The first category of the conventional endless track includes an iron link belt 1, an iron shoe 2 and a rubber pad (A-Type) 3, as illustrated in FIG. 14. The iron link belt 1 is provided with the iron shoe 2 which is formed independently of the iron link belt 1. Each iron shoe 2 is provided with the rubber pad (A-Type) 3 including an iron plate 3a and a rubber material 3b, which is adhered to the iron plate 3a through a vulcanization process.
The second category of the conventional endless track includes an iron link belt 1 and a rubber pad (B-Type) 4, as illustrated in FIG. 15. The iron link belt 1 includes a pair of links, to which a plate 4c is welded. The plate 4c is fastened to the rubber pad (B-Type) by a bolt or the like. The rubber pad (B-Type) includes a core metal plate 4a, and a rubber material 4b, which is adhered to the core metal plate 4a through a vulcanization process. The rubber pad (B-type) is directly fixed to the iron link belt 1 without employing an iron shoe. Therefore, the endless track of the second type does not include an iron shoe.
The third category of the conventional endless track includes a rubber crawler 5, as illustrated in FIG. 16. A plurality of iron core plates 5a are embedded in a single rubber belt 5, and the rubber 5b of the rubber belt 5 is adhered to the iron core plates 5a through a vulcanization process, while exposing a part of each iron core plate 5a. The rubber belt 5b extends endlessly. The endless track engages a sprocket at an exposed portion of each iron core plate 5a. Therefore, the endless track of the third category includes neither an iron link belt nor an iron shoe.
Hereinafter, the first category of the conventional endless track will be referred to hereafter as a rubber pad type A, the second category of the endless track will be referred to hereafter as a rubber pad type B, and the third category of the endless track will be referred to hereafter as a rubber crawler type.
The following problems exist in the conventional endless tracks of the type having the ground opposing surface made from rubber.
With the conventional endless track of the rubber pad type A (the first category), rubber needs to be vulcanization-adhered to the iron plate per each of the rubber pads, which requires much time and work, resulting in low productivity.
Further, the conventional endless track of the rubber pad type A requires a large number of members. Thus, the cost is high.
Similarly, with the conventional endless track of the rubber pad type B (the second category), rubber needs to be vulcanization-adhered to the core plate per each of the rubber pads, which requires much time and work, resulting in low productivity.
Although the number of members required for the rubber pad type B is smaller than that of the rubber pad type A because no shoes are included in the rubber pad type B, the rigidity is required all over the rubber pad, so that the manufacturing cost is almost the same as that of the conventional endless track of rubber pad type A.
With the conventional endless track of the rubber crawler type (the third category), the number of the members and the cost are reduced compared with those of the rubber pad type A and the rubber pad type B. However, because a tensile force is borne by the rubber belt only, the life of the rubber belt is relatively short. As a result, breakage of the rubber belt and derailment of the rubber belt are likely to occur during operation.
In order to solve the above problems, the applicant proposed, in Japanese Patent Application No. 2001-42920, an endless track of the type having a ground opposing surface made from rubber and a manufacturing method thereof, whereby the productivity in vulcanization-forming may be improved, the number of members may be reduced and the durability may be improved, as follows:                (a) An endless track comprising:        an iron link belt including a link unit assembly constructed of a plurality of link units connected to each other, each link unit including a pair of links;        a continuous pad including the same number of core metal plates as that of said plurality of link units and a single rubber belt, each of said core metal plates being fixed to each of said plurality of link units, said rubber belt covering and being vulcanization-adhered to a ground opposing surface of each of said core metal plates, said rubber belt being continuous over all of said core metal plates; and        a connecting device for connecting said iron link belt and said continuous pad at said link units and said core metal plates.        (b) A method for manufacturing an endless track comprising:        connecting a plurality of link units each having a pair of links thereby manufacturing a link unit assembly of an iron link belt; and        providing the same number of core metal plates as that of said plurality of link units of said iron link belt and forming a single rubber belt continuously extending over all of said core metal plates such that said single rubber belt covers and is vulcanization-adhered to a ground opposing surface of each of said core metal plates, thereby manufacturing a continuous pad.        
However, in the endless track of (a) and the method of (b), since a material of a rubber belt is constructed of vulcanized rubber, further improvement in durability has been desired.